In the industrialized countries, coronary heart disease (CHD) is the most frequent cause of heart failure. Coronary heart disease results in an inadequate supply of blood to the cardiac muscle and possibly to its necrotization because of narrowing of the coronary arteries. Despite much success with drug therapy, direct treatment of the triggering cause constitutes an important therapeutic concept. For CHD patients, the restoration of adequate perfusion by means of revascularization measures such as thrombolysis, stenting, balloon dilation, a bypass operation, etc. is therefore paramount. However, the success of these revascularization measures is dependent on the presence of a vital myocardium downstream of the arterial location treated. While revascularization of vital myocardial areas may improve the pumping function of the heart and the patient's prognosis, revascularization of scar tissue (necrotized) does not produce any improvement in results and constitutes additional risks for the patient.
Precise differentiation between vital and necrotic myocardium is therefore important for the further treatment of patients with an ischemic cardiomyopathy or after a myocardial infarction.
Myocardial tissue areas can be subdivided into the following categories:    (a) normally perfused, i.e. healthy myocardial tissue,    (b) less perfused myocardial tissue which is not or not yet necrotic and    (c) necrotic myocardial tissue (scar tissue).
The differentiation of myocardial tissue into these three groups is relevant to diagnosis and therapy in the field of interventional cardiology and also for electrical electrophysiology, as will be explained below.
Blockages in the coronary arteries which are found e.g. during computed tomography (CT) are nowadays opened using the above-mentioned revascularization measures, which applies to categories b and c. Blockages are therefore opened whose revascularization results in no improvement in the patient's condition, as the myocardial tissue to be supplied is already necrotic and therefore can no longer be reactivated (category c). These operations also pose a risk to the patient, are expensive and have no chance of improving the patient's condition. Only interventions which treat myocardial class b but not myocardial class c are therefore clinically induced. However, this requires reliable, image-based differentiation of the two categories.
Even in the case of electrophysiological ablation procedures for treating ventricular tachycardia (VT ablation) it is advantageous to know the precise position of contours of necrotic myocardial tissue areas, as the pathological conduction centers to be ablated are often in the immediate vicinity of these areas and must be selectively removed there by ablation.
Nowadays magnetic resonance tomography and particularly the nuclear medicine radionuclide techniques of single photon emission computed tomography (SPECT) and positron emission tomography (PET) are standard imaging methods for assessing myocardial vitality. Although new generations of CT scanners are able to record the heart in a breath-hold phase and therefore represent it in an artifact-free manner, they have hitherto had no role in assessing myocardial vitality, even though their basic advantages are known in the prior art.
In general, computed tomography imaging of the heart is the preferred imaging modality for patients with scarred myocardial regions, as pacemakers or implemented defibrillators which frequently occur in the patient profile assumed preclude the use of magnetic resonance imaging, and other modalities such as SPECT or PET provide significantly reduced local resolution. Moreover, using computed tomography is less expensive and its widespread availability even in emergency centers and the possibility of reliable assessment of the extent of the regions in question are further advantages.
It has been shown that if a contrast agent suitable for computed tomography is administered, in the case of a healthy heart the contrast agent is virtually completely eliminated again by the kidneys after a waiting time and a CT scan of the heart carried out after a certain time shows a native image without contrast agent. On the other hand, it has been shown that pathological changes such as stenoses may cause the contrast agent to penetrate much more slowly into the category b and/or c regions affected by the stenosis, but also to be flushed out of these areas more slowly than is the case with healthy tissue.
A possible option for imaging such areas is therefore so-called late enhancement scanning which is performed when a certain time t has elapsed between administration of the contrast agent and the subsequent CT scan, i.e. the CT scan is not performed immediately (in the range of seconds to minutes) after administration of the contrast agent. By detecting such contrast agent increases in late enhancement scan data, an unambiguous assessment is possible as to whether this tissue is myocardium of classification levels a or b (healthy and less perfused) or c (necrotic). Although waiting times of 5 or 15 minutes have been known in the prior art, these waiting times were arbitrarily set.
The problem when using computed tomography for visualizing necrotic myocardial areas lies in the patient-specific optimum waiting time t from administration of contrast agent to image capture in order to differentiate scar tissue in the myocardium.